1. Field of the Invention
This invention relates generally to the prevention or inhibition of the deleterious effects of sulfate reducing bacteria in aqueous environments, including both the contamination of process water and also the degradation and corrosion damage caused to metals and other material surfaces in contact with sulfate reducing bacteria, as often occurs in well drilling and production operations.
2. Description of the Prior Art
Both overall water quality and the degradation and corrosion damage to material infrastructures exposed to aqueous environments are ever growing concerns in today's world in a variety of different settings. Scientists now understand that microbes contribute significantly to degradation and corrosion damage. When surfaces, and particularly metals, are exposed to natural environments, they are rapidly colonized by aerobic bacteria present in the surrounding liquid environment which form a “biofilm.” The upper layers of this biofilm are thought to be aerobic while the regions near the metal surface are thought to be anaerobic due to the depletion of oxygen by the biofilm. Sulfate Reducing Bacteria (herein referred to as “SRB”) can colonize these anaerobic niches and thus contribute to corrosion even in an aerobic environment. SRB have been implicated in the deterioration of metals in a wide range of environments including pipelines and off-shore oil rigs in the oil and shipping industries. However, other environments are affected, as well, including cooling water recirculation systems in industrial settings and sewage treatment facilities and pipelines, to name a few. SRB can act in these and other systems to cause corrosion of a wide range of metals including low-grade carbon steels, but also including stainless steels, and other metals and metal alloys of the type which are commonly used in the chemical process, shipping, and power industries. SRB also cause various deleterious effects on nonmetallic systems and materials in some environments.
The complete nature of the operation of these microorganisms in causing damage to a variety of common infrastructure is not fully understood. However, it is known that SRB produce hydrogen sulfide, which is then metabolized by sulfur-oxidizing organisms such as Thiobacillus into sulfuric acid. Sulfuric acid degradation due to bacteria has been found to cause billions of dollars of corrosion damage in the U.S. each year alone.
Conventional corrosion inhibition strategies have included a variety of different strategies including, to name a few, modification in the pH, redox potential, and resistivity of the soil in which the equipment is to be installed, inorganic coatings, cathodic protection, and the use of “traditional” biocides. Inorganic protective coatings like paints and epoxies have been used extensively in the past; but, they are not permanent, and the cost of maintaining and replacing them is substantial. With cathodic protection, the cathodic reaction is stimulated on the metal surface by coupling it to a sacrificial anode, or by supplying an impressed current from an external power supply through a corrosion-resistant anode. Many of these strategies are not practical in well completion and production operations, however.
Traditional biocides have been used extensively to retard the corrosion reaction in closed systems such as cooling towers and storage tanks and are probably the most common method of combating biocorrosion. Oxidizing biocides like chlorine, chloramines, and chlorinating compounds are used in freshwater systems. Chlorine compounds are generally thought to be the most practical biocides; however, their activity depends on the pH of the water and the extent of light and temperature and they may not always be effective against biofilm bacteria. Non-oxidizing biocides such as quartenary salts, amine-type compounds, anthraquinones, and aldehydes are more stable and can be used in a variety of environments. Use of these biocides suffer from a number of serious drawbacks, including not only the cost of the biocides themselves, but also the environmental cost of releasing large quantities of these inorganic compounds into the water supply.
What is needed in the art is an effective, environmentally friendly, and economically acceptable means to prevent or inhibit SRB-caused water contamination and/or material infrastructure corrosion or degradation, with lessened release of toxic agents into the surrounding environment.